Photoacoustic measurement device

ABSTRACT

Provided is a photoacoustic measurement device including: an ultrasound image generation unit that generates an ultrasound image on the basis of a detection signal of reflected ultrasonic waves generated by the transmission of ultrasonic waves; a puncture needle detection unit that detects a length direction of a puncture needle on the basis of the ultrasound image; and a controller that controls a steering direction of a region of interest which is a color Doppler measurement target on the basis of the length direction of the puncture needle such that an angle θ formed between a straight line extending in the length direction of the puncture needle and a straight line extending in the steering direction of the region of interest satisfies 0°≤θ&lt;90°.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of InternationalApplication No. PCT/JP2017/033343, filed Sep. 14, 2017, the disclosureof which is incorporated herein by reference in its entirety. Further,this application claims priority from Japanese Patent Application No.2016-183785, filed Sep. 21, 2016, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND 1. Technical Field

The present invention relates to a photoacoustic measurement devicecomprising an insert of which at least a portion is inserted into asubject and which includes a photoacoustic wave generation portion thatabsorbs light and generates photoacoustic waves.

2. Related Art

An ultrasonography method has been known as a kind of image inspectionmethod that can non-invasively inspect the internal state of a livingbody. In ultrasonography, an ultrasound probe that can transmit andreceive ultrasonic waves is used. In a case in which the ultrasoundprobe transmits ultrasonic waves to a subject (living body), theultrasonic waves travel in the living body and are reflected from theinterface between tissues. The ultrasound probe receives the reflectedultrasonic waves and a distance is calculated on the basis of the timeuntil the reflected ultrasonic waves return to the ultrasound probe. Inthis way, it is possible to capture an image indicating the internalaspect of the living body.

In addition, photoacoustic imaging has been known which captures theimage of the inside of a living body using a photoacoustic effect. Ingeneral, in the photoacoustic imaging, the inside of the living body isirradiated with pulsed laser light. In the inside of the living body, aliving body tissue absorbs the energy of the pulsed laser light andultrasonic waves (photoacoustic waves) are generated by adiabaticexpansion caused by the energy. For example, an ultrasound probe detectsthe photoacoustic waves and a photoacoustic image is formed on the basisof a detection signal. In this way, it is possible to visualize theinside of the living body on the basis of the photoacoustic waves.

In addition, as a technique related to the photoacoustic imaging,JP2015-231583A discloses a puncture needle in which a photoacoustic wavegeneration portion that absorbs light and generates photoacoustic wavesis provided in the vicinity of a tip. In the puncture needle, an opticalfiber is provided up to the tip of the puncture needle and light guidedby the optical fiber is emitted to the photoacoustic wave generationportion. An ultrasound probe detects the photoacoustic waves generatedby the photoacoustic wave generation portion and a photoacoustic imageis generated on the basis of a detection signal of the photoacousticwaves. In the photoacoustic image, a part of the photoacoustic wavegeneration portion appears as a bight point, which makes it possible tocheck the position of the puncture needle using the photoacoustic image.

In addition, Doppler measurement has been known as a kind ofultrasonography. The Doppler measurement is a measurement method thatnon-invasively measures, for example, hemodynamics, a blood flow rate,and trends in vivo on the basis of the Doppler shift of the frequency ofreceived waves with respect to the frequency of transmitted waves.Examples of the Doppler measurement include pulsed Doppler measurementwhich transmits pulsed ultrasonic waves, detects reflected ultrasonicwaves, analyzes the Doppler shift of the reflected ultrasonic waves, anddisplays a waveform and color Doppler measurement which maps thedistribution of a blood flow rate and displays a color Doppler image.For example, JP2009-207588A discloses a technique that detects the tipof a puncture needle in an ultrasound image and sets a sample gate as apulsed Doppler measurement target in the vicinity of the tip, in orderto easily check a blood flow on a puncture needle guide in a case inwhich pulsed Doppler measurement is performed while the puncture needleis being used.

SUMMARY

Here, it is considered that the puncture needle generating photoacousticwaves disclosed in JP2015-231583A is used in order to check the positionof the tip of the puncture needle in a case in which ultrasonographyusing the puncture needle is performed.

However, in a case in which color Doppler measurement is performed usingthe puncture needle generating photoacoustic waves disclosed inJP2015-231583A, a color Doppler signal obtained by the color Dopplermeasurement is a weak signal. Therefore, in a case in which therelationship between an insertion direction of the puncture needle and asteering direction of a region of interest is not appropriately set, asignal caused by the reflected waves of the ultrasonic waves from thepuncture needle is included as an artifact in the color Doppler signalobtained by the color Doppler measurement, which makes it difficult toacquire an accurate color Doppler signal. Specifically, for example, asthe angle formed between the insertion direction (length direction) ofthe puncture needle and the steering direction of the region of interestbecomes closer to a right angle, the influence of the reflected wavesfrom the puncture needle on the color Doppler signal of the region ofinterest becomes larger.

In addition, JP2009-207588A does not disclose any technique consideringthe influence of the reflected waves from the puncture needle in a casein which a sample gate is set in the pulsed Doppler measurement.

The invention has been made in view of the above-mentioned problems andan object of the invention is to provide a photoacoustic measurementdevice that, in a case in which color Doppler measurement is performedwith an insert, such as a puncture needle that generates photoacousticwaves from a tip, can suppress the generation of an artifact caused byreflected waves from the insert.

According to the invention, there is provided a photoacousticmeasurement device comprising: an insert of which at least a tip portionis inserted into a subject and which includes a light guide member thatguides light to the tip portion and a photoacoustic wave generationportion that absorbs the light guided by the light guide member andgenerates photoacoustic waves; an acoustic wave detection unit thatdetects the photoacoustic waves generated from the photoacoustic wavegeneration portion and detects reflected acoustic waves reflected bytransmission of acoustic waves to the subject; a color Doppler signalgeneration unit that generates a color Doppler signal on the basis ofthe reflected acoustic waves from a region of interest as a colorDoppler measurement target which have been detected by the acoustic wavedetection unit; a reflected acoustic image generation unit thatgenerates a reflected acoustic image on the basis of the reflectedacoustic waves detected by the acoustic wave detection unit; an insertdetection unit that detects a length direction of the insert on thebasis of the reflected acoustic image; and a control unit that controlsa steering direction of the region of interest on the basis of thelength direction of the insert such that an angle θ formed between astraight line which extends in the length direction of the insert and astraight line which extends in the steering direction of the region ofinterest satisfies 0°≤θ<90°.

In the photoacoustic measurement device according to the invention, thecontrol unit may set the steering direction of the region of interest,following a change in an insertion direction of the insert, in a statein which a magnitude of the angle θ is maintained.

In the photoacoustic measurement device according to the invention, thecontrol unit may set the angle θ to 0°.

In the photoacoustic measurement device according to the invention, thecontrol unit may store a plurality of steering angle candidates of theregion of interest in advance and select a steering angle at which theangle θ satisfies 0°≤θ<90° and the steering direction of the region ofinterest is closest to the length direction of the insert from theplurality of steering angle candidates.

The photoacoustic measurement device according to the invention mayfurther comprise: a photoacoustic image generation unit that generates aphotoacoustic image on the basis of the photoacoustic waves detected bythe acoustic wave detection unit; and a tip position detection unit thatdetects a position of a tip of the insert on the basis of thephotoacoustic image. The control unit may control a position of theregion of interest such that the tip of the insert is included in theregion of interest.

In the photoacoustic measurement device according to the invention, thecontrol unit may control the position of the region of interest suchthat a center position of the region of interest is matched with the tipof the insert.

In the photoacoustic measurement device according to the invention, thecontrol unit may set the position of the region of interest, followingmovement of the position of the tip of the insert, in a state in which arelative positional relationship between the position of the tip of theinsert and the region of interest is maintained.

In the photoacoustic measurement device according to the invention, theinsert detection unit may detect the length direction of the insert ateach interval of two or more frames of the reflected acoustic images.

In the photoacoustic measurement device according to the invention, theinsert detection unit may acquire an amount of change in an angle of thelength direction of the insert. In a case in which the amount of changeis equal to or less than a predetermined threshold value, the insertdetection unit may increase the frame interval at which the lengthdirection of the insert is detected.

The photoacoustic measurement device according to the invention mayfurther comprise: a photoacoustic image generation unit that generates aphotoacoustic image on the basis of the photoacoustic waves detected bythe acoustic wave detection unit; and a tip position detection unit thatdetects a position of a tip of the insert on the basis of thephotoacoustic image. In a case in which the position of the tip of theinsert detected by the tip position detection unit is the same as aposition of the tip of the insert in the photoacoustic image of aprevious frame, the detection of the length direction of the insertbased on the reflected acoustic image and the control of the steeringdirection of the region of interest based on the length direction of theinsert may not be performed.

In the photoacoustic measurement device according to the invention, theinsert may be a needle that is inserted into the subject.

According to the photoacoustic measurement device of the invention, areflected acoustic image is generated on a detection signal of reflectedacoustic waves generated by the transmission of acoustic waves and thelength direction of the insert is detected on the basis of the reflectedacoustic image. The steering direction of the region of interest whichis a color Doppler measurement target is controlled on the basis of thelength direction of the insert such that the angle θ formed between thestraight line extending in the length direction of the insert and thestraight line extending in the steering direction of the region ofinterest satisfies 0°≤θ<90°. Therefore, it is possible to suppress thegeneration of an artifact in a color Doppler signal caused by thereflected waves from the insert.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments according to the technique of the presentdisclosure will be described in detail based on the following figures,wherein:

FIG. 1 is a block diagram schematically illustrating the configurationof a photoacoustic image generation apparatus using a first embodimentof a photoacoustic measurement device according to the invention;

FIG. 2 is a cross-sectional view illustrating the configuration of a tipportion of a puncture needle;

FIG. 3 is a flowchart illustrating a method for setting a steeringdirection of a region of interest in the photoacoustic image generationapparatus according to the first embodiment;

FIG. 4 is a diagram illustrating the method for setting the steeringdirection of the region of interest in the photoacoustic imagegeneration apparatus according to the first embodiment;

FIG. 5 is a block diagram schematically illustrating the configurationof a photoacoustic image generation apparatus using a second embodimentof the photoacoustic measurement device according to the invention;

FIG. 6 is a flowchart illustrating a method for setting the position andsteering direction of a region of interest in the photoacoustic imagegeneration apparatus according to the second embodiment;

FIG. 7 is a diagram illustrating the method for setting the position andsteering direction of the region of interest in the photoacoustic imagegeneration apparatus according to the second embodiment;

FIG. 8 is a diagram illustrating a method for controlling the turn-onand turn-off of a process of detecting a length direction of a punctureneedle on the basis of the amount of change in the angle of a lengthdirection of the puncture needle; and

FIG. 9 is a flowchart illustrating a method for controlling the turn-onand turn-off of the process of detecting the length direction of thepuncture needle on the basis of a change in the position of a tipportion of the puncture needle.

DETAILED DESCRIPTION

Hereinafter, a photoacoustic image generation apparatus using a firstembodiment of a photoacoustic measurement device according to theinvention will be described in detail with reference to the drawings.FIG. 1 is a diagram schematically illustrating the configuration of aphotoacoustic image generation apparatus 10 according to thisembodiment.

As illustrated in FIG. 1, the photoacoustic image generation apparatus10 according to this embodiment comprises an ultrasound probe 11, anultrasound unit 12, a laser unit 13, and a puncture needle 15. Thepuncture needle 15 and the laser unit 13 are connected by an opticalcable 16 having an optical fiber. The puncture needle 15 can be attachedto and detached from the optical cable 16 and is disposable. Inaddition, in this embodiment, ultrasonic waves are used as acousticwaves. However, the invention is not limited to the ultrasonic waves.Acoustic waves with an audible frequency may be used as long as anappropriate frequency can be selected according to, for example, aninspection target or measurement conditions.

The laser unit 13 comprises a solid-state laser light source using, forexample, yttrium aluminum garnet (YAG) and alexandrite. Laser lightemitted from the solid-state laser light source of the laser unit 13 isguided by the optical cable 16 and is incident on the puncture needle15. The laser unit 13 according to this embodiment emits pulsed laserlight in a near-infrared wavelength range. The near-infrared wavelengthrange means a wavelength range from about 700 nm to 850 nm. In thisembodiment, the solid-state laser light source is used. However, otherlaser light sources, such as a gas laser light source, may be used orlight sources other than the laser light source may be used.

The puncture needle 15 is an embodiment of an insert according to theinvention and is a needle that is inserted into a subject M. FIG. 2 is across-sectional view including a center axis that extends in a lengthdirection of the puncture needle 15. The puncture needle 15 includes apuncture needle main body 15 a that has an opening at an acute tip andis formed in a hollow shape, an optical fiber 15 b (corresponding to alight guide member according to the invention) that guides laser lightemitted from the laser unit 13 to the vicinity of the opening of thepuncture needle 15, and a photoacoustic wave generation portion 15 cthat absorbs laser light emitted from the optical fiber 15 b andgenerates photoacoustic waves.

The optical fiber 15 b and the photoacoustic wave generation portion 15c are provided in a hollow portion 15 d of the puncture needle main body15 a. For example, the optical fiber 15 b is connected to the opticalfiber in the optical cable 16 (see FIG. 1) through an optical connectorthat is provided at the base end of the puncture needle 15. For example,a laser light of 0.2 mJ is emitted from a light emission end of theoptical fiber 15 b.

The photoacoustic wave generation portion 15 c is provided at the lightemission end of the optical fiber 15 b and is provided in the vicinityof the tip of the puncture needle 15 and in the inner wall of thepuncture needle main body 15 a. The photoacoustic wave generationportion 15 c absorbs the laser light emitted from the optical fiber 15 band generates photoacoustic waves. The photoacoustic wave generationportion 15 c is made of, for example, an epoxy resin, a polyurethaneresin, a fluorine resin, and silicone rubber with which a black pigmentis mixed. In FIG. 2, the photoacoustic wave generation portion 15 c isillustrated to be larger than the optical fiber 15 b. However, theinvention is not limited thereto. The photoacoustic wave generationportion 15 c may have a size that is equal to the diameter of theoptical fiber 15 b.

The photoacoustic wave generation portion 15 c is not limited to theabove and a metal film or an oxide film having light absorptivity withrespect to the wavelength of laser light may be used as thephotoacoustic wave generation portion. An oxide film made of, forexample, iron oxide, chromium oxide, or manganese oxide having highlight absorptivity with respect to the wavelength of laser light can beused as the photoacoustic wave generation portion 15 c. Alternatively, ametal film made of, for example, titanium (Ti) or platinum (Pt) that hasa lower light absorptivity than an oxide and has a higherbiocompatibility than an oxide may be used as the photoacoustic wavegeneration portion 15 c. In addition, the position where thephotoacoustic wave generation portion 15 c is provided is not limited tothe inner wall of the puncture needle main body 15 a. For example, ametal film or an oxide film which is the photoacoustic wave generationportion 15 c may be formed on the light emission end of the opticalfiber 15 b with a thickness of about 100 nm by vapor deposition suchthat the oxide film covers the light emission end. In this case, atleast a portion of the laser light emitted from the light emission endof the optical fiber 15 b is absorbed by the metal film or the oxidefilm covering the light emission end and photoacoustic waves aregenerated from the metal film or the oxide film.

The vicinity of the tip of the puncture needle 15 means a position wherethe photoacoustic wave generation portion 15 c can generatephotoacoustic waves capable of imaging the position of the tip of thepuncture needle 15 with accuracy required for a needling operation in acase in which the tip of the optical fiber 15 b and the photoacousticwave generation portion 15 c are disposed at the position. For example,the vicinity of the tip of the puncture needle 15 is the range of 0 mmto 3 mm from the tip to the base end of the puncture needle 15. In thesubsequent embodiments, the meaning of the vicinity of the tip is thesame as described above.

Returning to FIG. 1, the ultrasound probe 11 corresponds to an acousticwave detection unit according to the invention and includes, forexample, a plurality of ultrasound transducers which areone-dimensionally arranged. The ultrasound transducer is, for example, apiezoelectric element made of a polymer film, such as piezoelectricceramics or polyvinylidene fluoride (PVDF).

The ultrasound probe 11 detects the photoacoustic waves generated fromthe photoacoustic wave generation portion 15 c after the puncture needle15 is inserted into a subject M. In addition, the ultrasound probe 11performs the transmission of ultrasonic waves (acoustic waves) to thesubject M and the detection of reflected ultrasonic waves (reflectedacoustic waves) with respect to the transmitted ultrasonic waves, inaddition to the detection of the photoacoustic waves.

In a case in which color Doppler measurement is performed, theultrasound probe 11 transmits pulsed ultrasonic waves and detectsreflected ultrasonic waves with respect to the pulsed ultrasonic waves.In addition, in a case in which color Doppler measurement is performed,the ultrasound probe 11 sets the position and steering direction of aregion of interest (hereinafter, referred to as an ROI), which is acolor Doppler measurement target, with respect to the subject M andtransmits ultrasonic waves in the steering direction of the ROI underthe control of a control unit 28.

For example, a linear ultrasound probe, a convex ultrasound probe, or asector ultrasound probe may be used as the ultrasound probe 11.

The ultrasound unit 12 includes a receiving circuit 20, a receivingmemory 21, a data demultiplexing unit 22, a color Doppler signalgeneration unit 23, a photoacoustic image generation unit 24, anultrasound image generation unit 25, an output unit 26, a transmissioncontrol circuit 27, the control unit 28, and a puncture needle detectionunit 31. The ultrasound unit 12 typically includes, for example, aprocessor, a memory, and a bus. A program related to, for example, acolor Doppler signal generation process, a photoacoustic imagegeneration process, an ultrasound image generation process, and aprocess of detecting the length direction of the puncture needle 15 inan ultrasound image is incorporated into a memory in the ultrasound unit12. The program is executed by the control unit 28 which is formed by aprocessor to implement the functions of the data demultiplexing unit 22,the color Doppler signal generation unit 23, the photoacoustic imagegeneration unit 24, the ultrasound image generation unit 25, the outputunit 26, and the puncture needle detection unit 31. That is, each ofthese units is formed by the processor and the memory into which theprogram has been incorporated.

The hardware configuration of the ultrasound unit 12 is not particularlylimited and can be implemented by an appropriate combination of, forexample, a plurality of integrated circuits (ICs), a processor, anapplication specific integrated circuit (ASIC), a field-programmablegate array (FPGA), and a memory.

The receiving circuit 20 receives a detection signal output from theultrasound probe 11 and stores the received detection signal in thereceiving memory 21. The receiving circuit 20 typically includes alow-noise amplifier, a variable-gain amplifier, a low-pass filter, andan analog-to-digital converter (AD converter). The detection signal ofthe ultrasound probe 11 is amplified by the low-noise amplifier. Then,gain adjustment corresponding to a depth is performed by thevariable-gain amplifier and a high-frequency component of the detectionsignal is cut by the low-pass filter. Then, the detection signal isconverted into a digital signal by the AD convertor and the digitalsignal is stored in the receiving memory 21. The receiving circuit 20 isformed by, for example, one integral circuit (IC).

The ultrasound probe 11 outputs a detection signal of the photoacousticwaves and a detection signal of the reflected ultrasonic waves. TheAD-converted detection signals (sampling data) of the photoacousticwaves and the reflected ultrasonic waves are stored in the receivingmemory 21.

In a case in which a photoacoustic image is generated, the datademultiplexing unit 22 reads the detection signal of the photoacousticwaves from the receiving memory 21 and transmits the detection signal tothe photoacoustic image generation unit 24. In addition, in a case inwhich an ultrasound image is generated, the data demultiplexing unit 22reads the detection signal of the reflected ultrasonic waves from thereceiving memory 21 and transmits the detection signal to the ultrasoundimage generation unit 25. Further, in a case in which color Dopplermeasurement is performed, the data demultiplexing unit 22 reads adetection signal of reflected ultrasonic waves from the ROI set by thecontrol unit 28 and transmits the detection signal to the color Dopplersignal generation unit 23.

The color Doppler signal generation unit 23 analyzes Doppler transitionin the ROI on the basis of the detection signal of the reflectedultrasonic waves generated by the transmission of the pulsed ultrasonicwaves to generate a color Doppler signal obtained by two-dimensionallymapping a distribution of a blood flow rate.

The photoacoustic image generation unit 24 generates a photoacousticimage on the basis of the detection signal of the photoacoustic wavesdetected by the ultrasound probe 11. The photoacoustic image generationprocess includes, for example, image reconfiguration, such as phasingaddition, detection, and logarithmic conversion.

The ultrasound image generation unit 25 (corresponding to a reflectedacoustic image generation unit according to the invention) generates anultrasound image (reflected acoustic image) on the basis of thedetection signal of the reflected ultrasonic waves detected by theultrasound probe 11. The ultrasound image generation process includesimage reconfiguration, such as phasing addition, detection, andlogarithmic conversion.

The output unit 26 displays the photoacoustic image and the ultrasoundimage on a display unit 30 such as a display device. In addition, theoutput unit 26 displays a color Doppler image obtained bytwo-dimensionally mapping the distribution of the blood flow rate on thedisplay unit 30 on the basis of the color Doppler signal. Further, theultrasound image and the color Doppler image may be displayed so as tobe superimposed on each other. Furthermore, a photoacoustic image may bedisplayed so as be superimposed on the ultrasound image and the colorDoppler image.

The puncture needle detection unit 31 corresponds to an insert detectionunit according to the invention, detects an image of the puncture needle15 from the ultrasound image generated by the ultrasound imagegeneration unit 25 on the basis of the ultrasound image, and detects thelength direction of the puncture needle 15 on the basis of the image. Asa method for detecting the image of the puncture needle 15, for example,a binarization process is performed for the ultrasound image and aregion in which white pixels are continuously distributed may bedetected as an image region of the puncture needle 15. In addition, theinvention is not limited thereto and the image of the puncture needle 15may be detected by other known types of image processing.

The control unit 28 controls each component in the ultrasound unit 12.For example, in a case in which a photoacoustic image is acquired, thecontrol unit 28 transmits a trigger signal to the laser unit 13 suchthat the laser unit 13 emits pulsed laser light. In addition, thecontrol unit 28 transmits a sampling trigger signal to the receivingcircuit 20 to control, for example, the sampling start time of thephotoacoustic waves with the emission of the laser light. The detectionsignal of the photoacoustic waves which has been received by thereceiving circuit 20 and then converted into a digital signal is storedin the receiving memory 21.

In a case in which an ultrasound image is acquired, the control unit 28transmits an ultrasound transmission trigger signal for commanding thetransmission of ultrasonic waves to the transmission control circuit 27.In a case in which the ultrasound transmission trigger signal isreceived, the transmission control circuit 27 directs the ultrasoundprobe 11 to transmit ultrasonic waves. The control unit 28 transmits thesampling trigger signal to the receiving circuit 20 according to thetransmission time of ultrasonic waves such that the receiving circuit 20starts the sampling of the reflected ultrasonic waves. The detectionsignal of the ultrasonic waves which has been received by the receivingcircuit 20 and then converted into a digital signal is stored in thereceiving memory 21.

In a case in which color Doppler measurement is performed, the controlunit 28 transmits a pulsed ultrasound transmission trigger signal forcommanding the transmission of pulsed ultrasonic waves to thetransmission control circuit 27. In a case in which the pulsedultrasound transmission trigger signal is received, the transmissioncontrol circuit 27 directs the ultrasound probe 11 to transmit pulsedultrasonic waves. The control unit 28 transmits the sampling triggersignal to the receiving circuit 20 according to the transmission time ofpulsed ultrasonic waves such that the receiving circuit 20 starts thesampling of the reflected ultrasonic waves. The detection signal of theultrasonic waves which has been received by the receiving circuit 20 andthen converted into a digital signal is stored in the receiving memory21.

In addition, in a case in which color Doppler measurement is performed,the control unit 28 sets the ROI which is a color Doppler measurementtarget as described above. Then, the control unit 28 sets the steeringdirection of the ROI and controls the ultrasound probe 11 such thatultrasonic waves are transmitted in the steering direction of the ROI.Then, the color Doppler signal generation unit 23 generates a colorDoppler signal on the basis of the positional information of the ROI setby the control unit 28.

Here, in a case in which needling is performed with the puncture needle15 having the photoacoustic wave generation portion 15 c as describedabove and color Doppler measurement is performed by a color Dopplermethod, if the insertion direction (length direction) of the punctureneedle 15 and the steering direction of the ROI are not appropriatelyset, a signal caused by reflected waves from the puncture needle 15 isincluded as an artifact in the detection signal of the reflectedultrasonic waves in the color Doppler measurement, which makes itdifficult to acquire an accurate color Doppler signal.

For this reason, the control unit 28 according to this embodiment setsthe steering direction of the ROI to an appropriate direction in orderto suppress the generation of the artifact. Hereinafter, a method forsetting the steering direction of the ROI in the control unit 28 will bedescribed with reference to a flowchart illustrated in FIG. 3 and FIG.4.

First, the control unit 28 sets the initially set position and steeringdirection of the ROI (S10). The initially set position and steeringdirection of the ROI may be stored in advance or the information of theinitially set position and steering direction of the ROI may be set andinput by the user, such as a doctor, through an input unit 40 (see FIG.1). In addition, an ultrasound image may be displayed on the displayunit 30 (see FIG. 1) such that the user sets and inputs the initiallyset position and steering direction of the ROI in the ultrasound imagewith the input unit 40. In addition, the initially set position of theROI is set to a position where a blood vessel is assumed to be presentin the subject M and the steering direction of the ROI is set to adirection assumed to be parallel to, for example, a direction in whichthe blood vessel extends.

Then, the control unit 28 checks whether the user has input a command tostart the detection of the angle of the puncture needle 15. In a case inwhich the angle detection start command has been input (S12, YES), thecontrol unit 28 starts a process of detecting the length direction ofthe puncture needle 15 (S14). In addition, the user inputs the angledetection start command and an angle detection end command with theinput unit 40 (see FIG. 1).

Specifically, ultrasonic waves are transmitted from the ultrasound probe11 to the subject M and a detection signal of reflected ultrasonic wavesdetected by the ultrasound probe 11 is received by the receiving circuit20 and is stored in the receiving memory 21 under the control of thecontrol unit 28. Then, the data demultiplexing unit 22 transmits thedetection signal of the reflected ultrasonic waves from the receivingmemory 21 to the ultrasound image generation unit 25 and the ultrasoundimage generation unit 25 generates an ultrasound image of one frame.

The ultrasound image of one frame generated by the ultrasound imagegeneration unit 25 is input to the puncture needle detection unit 31 andthe puncture needle detection unit 31 detects the length direction ofthe puncture needle 15 (S14).

Then, the information of the length direction of the puncture needle 15detected by the puncture needle detection unit 31 is input to thecontrol unit 28. As illustrated in FIG. 4, the control unit 28calculates an angle θ formed between a straight line L1 which extends inthe length direction of the puncture needle 15 and a straight line L2which extends in the initially set steering direction of the ROI on thebasis of the input information of the length direction of the punctureneedle 15 and checks whether the angle θ is greater than a predeterminedthreshold value θth.

Here, in the invention, the angle formed between the straight line whichextends in the length direction of the insert and the straight linewhich extends in the steering direction of the ROI means an angle formedbetween a straight line which extends in the length direction of thepuncture needle 15 from an insertion starting point of the punctureneedle 15 and a straight line which extends in the steering directionfrom the incident side of ultrasonic waves in a case in which anintersection point of the straight line L1 extending in the lengthdirection of the insert (puncture needle 15) and the straight line L2extending in the steering direction of the ROI is a vertex V asillustrated in FIG. 4.

In addition, a value satisfying 0°≤θth<90° is set as the threshold valueθth. Most preferably, θth is 0°. However, a value satisfying 0°<θth≤10°,a value satisfying 0°<θth≤15°, a value satisfying 0°<θth≤30°, or a valuesatisfying 0°<θth≤45° may be set. In a case in which the threshold valueθth is 0°, checking whether the angle θ is greater than the thresholdvalue θth is synonymous with checking whether the straight line L1 andthe straight line L2 are parallel to each other.

Then, in a case in which the angle θ is equal to or less than thethreshold value θth (S16, NO), the control unit 28 determines that theinsertion direction (length direction) of the puncture needle 15 and thesteering direction of the ROI are appropriate and performs color Dopplermeasurement while maintaining the initially set position and steeringdirection of the ROI (S20).AA

Specifically, the ultrasound probe 11 transmits pulsed ultrasonic waves.Then, the ultrasound probe 11 detects reflected ultrasonic wavesgenerated by the transmission of the pulsed waves. Then, a detectionsignal of the reflected ultrasonic waves is received by the receivingcircuit 20 and is stored in the receiving memory 21. Then, the datademultiplexing unit 22 transmits the detection signal of the reflectedultrasonic waves from the receiving memory 21 to the color Dopplersignal generation unit 23. The color Doppler signal generation unit 23generates a color Doppler signal on the basis of the initially setinformation of the ROI. Then, the output unit 26 displays a colorDoppler image based on the color Doppler signal the display unit 30.

On the other hand, in a case in which the angle θ is greater than thethreshold value θth in S16 (S16, YES), the control unit 28 sets thesteering direction of the ROI on the basis of the length direction ofthe puncture needle 15 detected by the puncture needle detection unit 31(S18). Specifically, the control unit 28 sets the steering direction ofthe ROI such that the angle θ formed between the straight line L1extending in the length direction of the puncture needle 15 and thestraight line L2 extending in the steering direction of the ROI is thethreshold value θth as illustrated in FIG. 4. Then, after the steeringdirection of the ROI is set, the control unit 28 performs color Dopplermeasurement in the same way as described above (S20). In addition, inthis embodiment, it is assumed that the position of the ROI is theinitial set position of the ROI.

Then, the control unit 28 checks whether the user has input a command toend the detection of the angle of the puncture needle 15 (S22). In acase in which the angle detection end command has not been input (S22,NO), the control unit 28 detects the length direction of the punctureneedle 15 on the basis of an ultrasound image of the next frame (S24).Then, the control unit 28 sets the steering direction of the ROI on thebasis of the length direction of the puncture needle 15 in theultrasound image of the next frame (S18). Specifically, similarly to theabove, the control unit 28 sets the steering direction of the ROI suchthat the angle θ formed between the straight line L1 extending in thelength direction of the puncture needle 15 and the straight line L2extending in the steering direction of the ROI is the threshold valueθth. Then, after the steering direction of the ROI is set, the controlunit 28 performs color Doppler measurement in the same way as describedabove (S20).

Then, in S22, the control unit 28 repeatedly performs the detection ofthe length direction of the puncture needle 15 in S24, the setting ofthe steering direction of the ROI in S18, and the color Dopplermeasurement in S20 until the user inputs a command to end the detectionof the angle of the puncture needle 15. The control unit 28 performsthis process to set the steering direction of the ROI, following achange in the insertion direction of the puncture needle 15, in a statein which the angle θ formed between the straight line L1 extending inthe length direction of the puncture needle 15 and the straight line L2extending in the steering direction of the ROI is maintained at thethreshold value θth.

Then, in a case in which the angle detection end command is input in S22(S22, YES), the control unit 28 ends the process.

The photoacoustic image generation apparatus 10 according to the firstembodiment generates an ultrasound image on the basis of the detectionsignal of the reflected ultrasonic waves generated by the transmissionof ultrasonic waves, detects the length direction of the puncture needle15 on the basis of the ultrasound image, and controls the steeringdirection of the ROI which is a color Doppler measurement target on thebasis of the length direction of the puncture needle 15 such that theangle θ formed between the straight line extending in the lengthdirection of the puncture needle 15 and the straight line extending inthe steering direction of the ROI satisfies 0°≤θ<90°. Therefore, it ispossible to suppress the generation of an artifact of a color Dopplersignal caused by the reflected waves from the puncture needle 15.

In the photoacoustic image generation apparatus 10 according to thefirst embodiment, in a case in which the angle θ is greater than thethreshold value θth, the steering direction of the ROI is set such thatthe angle θ is the threshold value θth. However, the invention is notlimited thereto. For example, the control unit 28 may store a pluralityof steering angle candidates of the ROI, select a steering anglecandidate at which the angle θ satisfies 0°≤θ<90° and the steeringdirection of the ROI is closest to the length direction of the punctureneedle 15 from the plurality of steering angle candidates, and set thesteering direction of the ROI to the direction indicated by the selectedsteering angle. In addition, the steering angle of the ROI is an angleindicating the inclination of the steering direction of the ROI withrespect to the depth direction of the subject M and is, for example, anangle of +α or −α illustrated in FIG. 4. As the steering anglecandidates, for example, ±10°, ±20°, and ±30° are stored in the controlunit 28 in advance. As described above, the control unit 28 sets onesteering angle from the steering angle candidates and sets the steeringdirection of the ROI to the direction indicated by the steering angle.

Next, a photoacoustic image generation apparatus 10 using a secondembodiment of the photoacoustic measurement device according to theinvention will be described. In the photoacoustic image generationapparatus 10 according to the first embodiment, in a case in which thesteering direction of the ROI is set on the basis of the lengthdirection of the puncture needle 15, the position of the ROI is theinitially set position of the ROI. However, the photoacoustic imagegeneration apparatus 10 according to the second embodiment controls theposition of the ROI.

FIG. 5 is a block diagram illustrating the configuration of thephotoacoustic image generation apparatus 10 according to the secondembodiment. As illustrated in FIG. 5, the photoacoustic image generationapparatus 10 according to the second embodiment differs from thephotoacoustic image generation apparatus 10 according to the firstembodiment in that it further comprises a tip position detection unit29. The other configurations are the same as those in the photoacousticimage generation apparatus 10 according to the first embodiment.

The tip position detection unit 29 detects the position of the tip ofthe puncture needle 15 on the basis of the photoacoustic image generatedby the photoacoustic image generation unit 24. As a method for detectingthe position of the tip of the puncture needle 15, for example, a methodmay be used which detects the position of a maximum brightness point inthe photoacoustic image as the position of the tip of the punctureneedle 15.

In a case in which the position of the tip of the puncture needle 15 isdetected on the basis of the photoacoustic image as described above, inpractice, an artifact of light or an artifact of sound is generated anda photoacoustic image in which photoacoustic waves are detected from aplurality of positions is likely to be generated and the originalposition of the tip of the puncture needle 15 is unlikely to bespecified.

For this reason, the photoacoustic image generated by the photoacousticimage generation unit 24 is not used as it is, but, for example, asmoothing process may be performed for the photoacoustic image toprevent erroneous detection caused by the artifact. Specifically, thesmoothing process is performed for the photoacoustic image subjected todetection and logarithmic conversion. For example, a filtering processusing a Gaussian filter can be used as the smoothing process.

Then, a binarization process is performed for the photoacoustic imagesubjected to the smoothing process to generate a binary image. Then, aregion in which white pixels are continuously distributed is detectedfrom the binary image to detect the position of the tip of the punctureneedle 15. In this way, it is possible to detect the position of the tipof the puncture needle 15 with higher accuracy.

Next, a method for setting the position of an ROI in the photoacousticimage generation apparatus 10 according to the second embodiment will bedescribed with reference to a flowchart illustrated in FIG. 6 and FIG.7.

In the photoacoustic image generation apparatus 10 according to thesecond embodiment, first, the control unit 28 sets the initially setposition and steering direction of the ROI (S30). A method for settingthe initially set position and steering direction of the ROI is the sameas that in the first embodiment.

Then, the control unit 28 checks whether the user has input a command tostart the detection of the angle of the puncture needle 15. In a case inwhich the angle detection start command has been input (S32, YES), thecontrol unit 28 starts a process of detecting the length direction ofthe puncture needle 15 (S34).

Specifically, similarly to the first embodiment, ultrasonic waves aretransmitted from the ultrasound probe 11 to the subject M and adetection signal of reflected ultrasonic waves detected by theultrasound probe 11 is received by the receiving circuit 20 and isstored in the receiving memory 21 under the control of the control unit28. Then, the data demultiplexing unit 22 transmits the detection signalof the reflected ultrasonic waves from the receiving memory 21 to theultrasound image generation unit 25 and the ultrasound image generationunit 25 generates an ultrasound image of one frame.

Then, the ultrasound image of one frame generated by the ultrasoundimage generation unit 25 is input to the puncture needle detection unit31 and the puncture needle detection unit 31 detects the lengthdirection of the puncture needle 15 (S34).

Then, the information of the length direction of the puncture needle 15detected by the puncture needle detection unit 31 is input to thecontrol unit 28. As illustrated in FIG. 7, the control unit 28calculates an angle θ formed between a straight line L1 which extends inthe length direction of the puncture needle 15 and a straight line L2which extends in the initially set steering direction of the ROI on thebasis of the input information of the length direction of the punctureneedle 15 and checks whether the angle θ is greater than a predeterminedthreshold value θth.

Then, in a case in which the angle θ is equal to or less than thethreshold value θth (S36, NO), the control unit 28 determines that theinsertion direction (length direction) of the puncture needle 15 and thesteering direction of the ROI are appropriate and does not change theinitially set steering direction of the ROI.

Then, a process of detecting the tip of the puncture needle 15 isperformed (S38). Specifically, a detection signal of the photoacousticwaves generated from the photoacoustic wave generation portion 15 c ofthe puncture needle 15 is received by the receiving circuit 20 and isstored in the receiving memory 21 under the control of the control unit28. Then, the data demultiplexing unit 22 transmits the detection signalof the photoacoustic waves from the receiving memory 21 to thephotoacoustic image generation unit 24 and the photoacoustic imagegeneration unit 24 generates a photoacoustic image of one frame.

The photoacoustic image of one frame generated by the photoacousticimage generation unit 24 is input to the tip position detection unit 29.The tip position detection unit 29 detects the position of a tip portionof the puncture needle 15.

Then, as illustrated in FIG. 7, the control unit 28 sets the position ofthe ROI such that a tip P of the puncture needle 15 is included in theROI (S40). In this embodiment, the position of the ROI is set such thata center position C of the ROI is matched with the tip P of the punctureneedle 15. However, the invention is not limited thereto. A positionother than the center position C may be matched with the tip P of thepuncture needle 15.

Then, after the position of the ROI is set as described above, colorDoppler measurement is performed in the same way as described above(S46).

On the other hand, in a case in which the angle θ is greater than thethreshold value θth in S36, (S36, YES), a process of detecting the tipof the puncture needle 15 is performed in the same way as describedabove (S42).

Then, the control unit 28 sets the steering direction and position ofthe ROI on the basis of the position of the tip of the puncture needle15 and the length direction of the puncture needle 15 detected by thepuncture needle detection unit 31 (S44). Specifically, similarly to thefirst embodiment, the control unit 28 sets the steering direction of theROI such that the angle θ formed between the straight line L1 extendingin the length direction of the puncture needle 15 and the straight lineL2 extending in the steering direction of the ROI is the threshold valueθth as illustrated in FIG. 7. In addition, the control unit 28 sets theposition of the ROI such that the tip P of the puncture needle 15 isincluded in the ROI as illustrated in FIG. 7.

Then, after the position and steering direction of the ROI are set,color Doppler measurement is performed in the same way as describedabove (S46).

Then, the control unit 28 checks whether the user has input a command toend the detection of the angle of the puncture needle 15 (S48). In acase in which the angle detection end command has not been input (S48,NO), the control unit 28 detects the length direction of the punctureneedle 15 on the basis of an ultrasound image of the next frame (S50).Then, the control unit 28 detects the position of the tip of thepuncture needle 15 on the basis of a photoacoustic image of the nextframe (S42).

Then, the control unit 28 sets the steering direction of the ROI on thebasis of the length direction of the puncture needle 15 in theultrasound image of the next frame and sets the position of the ROI onthe basis of the position of the tip of the puncture needle 15 in thephotoacoustic image of the next frame (S44). Then, after the positionand steering direction of the ROI are set, color Doppler measurement isperformed in the same way as described above (S46).

Then, in S48, the control unit 28 repeatedly performs the detection ofthe length direction of the puncture needle 15 in S50, the detection ofthe position of the tip of the puncture needle 15 in S42, the setting ofthe position and steering direction of the ROI in S44, and the colorDoppler measurement in S46 until the user inputs a command to end thedetection of the angle of the puncture needle 15. The control unit 28performs this process to set the steering direction of the ROI,following a change in the insertion direction of the puncture needle 15,in a state in which the angle θ formed between the straight line L1extending in the length direction of the puncture needle 15 and thestraight line L2 extending in the steering direction of the ROI ismaintained at the threshold value θth. In addition, the control unit 28can set the position of the ROI, following the movement of the positionof the tip of the puncture needle 15, in a state in which the relativepositional relationship between the position of the tip of the punctureneedle 15 and the ROI is maintained. Therefore, it is possible to alwaysset the ROI, which is a color Doppler measurement target, in thevicinity of the tip of the puncture needle 15 and thus to immediatelycheck the distribution of a blood flow rate in the vicinity of the tipof the puncture needle 15.

Then, in a case in which the angle detection end command is input in S48(S48, YES), the control unit 28 ends the process.

In the photoacoustic image generation apparatus 10 according to thesecond embodiment, for each frame for acquiring an ultrasound image, thelength direction of the puncture needle 15 is detected on the basis ofthe ultrasound image. However, since the length direction of thepuncture needle 15 is not frequently changed, it is not necessary todetect the length direction of the puncture needle 15 for each frame.Therefore, the length direction of the puncture needle 15 may bedetected at each interval of two or more frames. In this case, it ispossible to reduce the load of the detection process of the punctureneedle 15.

In addition, the puncture needle detection unit 31 may acquire theamount of change in the angle of the length direction of the punctureneedle 15 on the basis of the length direction of the puncture needle 15and the frame interval at which the process of detecting the lengthdirection of the puncture needle 15 is performed may be increased in acase in which the amount of change is equal to or less than apredetermined threshold value. In a case in which there is no change inthe angle of the length direction of the puncture needle 15, the processof detecting the length direction of the puncture needle 15 may not beperformed (may be omitted) for a reflected acoustic image of the nextframe. FIG. 8 is a diagram illustrating an example of a case in whichthe timing of the process of detecting the length direction of thepuncture needle 15 is controlled as described above. Here, the angle ofthe length direction of the puncture needle 15 means an acute angleamong the angles formed between a straight line extending in the lengthdirection of the puncture needle 15 and a straight line extending in thedepth direction.

As illustrated in FIG. 8, in a second frame, there is no change in theangle of the length direction of the puncture needle 15 from a firstframe. Therefore, in a third frame, the process of detecting the lengthdirection of the puncture needle 15 is not performed. In a fourth frame,the process of detecting the length direction of the puncture needle 15is performed again. However, since the angle has not been changed fromthe previously detected angle, the process of detecting the lengthdirection of the puncture needle 15 is not performed in the fifth andsixth frames. That is, the frame interval at which the process ofdetecting the length direction of the puncture needle 15 is notperformed is increased. Then, in a seventh frame, the process ofdetecting the length direction of the puncture needle 15 is performedagain. However, since the angle has not been changed from the previouslydetected angle, the frame interval at which the process of detecting thelength direction of the puncture needle 15 is not performed is furtherincreased. That is, the process of detecting the length direction of thepuncture needle 15 is not performed in three frames, that is, eighth totenth frames.

Then, in an eleventh frame, the process of detecting the lengthdirection of the puncture needle 15 is performed again. In the processof detecting the length direction of the puncture needle 15 for theeleventh frame, the angle has been changed from the previously detectedangle. Therefore, in a twelfth frame, the process of detecting thelength direction of the puncture needle 15 is also performed. In theprocess of detecting the length direction of the puncture needle 15 forthe twelfth frame, the angle has been changed from the previouslydetected angle. Therefore, in a thirteenth frame, the process ofdetecting the length direction of the puncture needle 15 is alsoperformed. In the process of detecting the length direction of thepuncture needle 15 for the thirteenth frame, the angle has been changedfrom the previously detected angle. Therefore, in a fourteenth frame,the process of detecting the length direction of the puncture needle 15is also performed. Since the angle has not been changed from thepreviously detected angle in the fourteenth frame, the process ofdetecting the length direction of the puncture needle 15 is notperformed in a fifteenth frame. Then, in a sixteenth frame, the processof detecting the length direction of the puncture needle 15 is performedagain. However, since the angle has not been changed from the previouslydetected angle, the process of detecting the length direction of thepuncture needle 15 is not performed in seventeenth and eighteenthframes. Then, in a nineteenth frame, the process of detecting the lengthdirection of the puncture needle 15 is performed again. However, sincethe angle has not been changed from the previously detected angle, theprocess of detecting the length direction of the puncture needle 15 isnot performed in a twentieth frame.

In the photoacoustic image generation apparatus 10 according to thesecond embodiment, in the process of detecting the position of the tipof the puncture needle 15, in a case in which the position of the tip ofthe puncture needle 15 has not been changed from the position of the tipin the photoacoustic image of the previous frame, the process ofdetecting the length direction of the puncture needle 15 and the processof setting the position and steering direction of the ROI on the basisof the position of the tip of the puncture needle 15 and the lengthdirection of the puncture needle 15 may not be performed (may beomitted). FIG. 9 is a flowchart in this case.

In the flowchart illustrated in FIG. 9, a process in S60 and S62 and S64to S76 based on an ultrasound image and a photoacoustic image of theinitial frame is the same as that in the second embodiment.

Then, the tip of the puncture needle 15 is detected on the basis of thephotoacoustic images of the second and subsequent frames (S80). At thattime, in a case in which the position of the tip has not been changedfrom the position of the tip in the photoacoustic image of the previousframe (S82, NO), the process of detecting the length direction of thepuncture needle 15 in S84 and the process of setting the position andsteering direction of the ROI in S74 are not performed and color Dopplermeasurement is performed (S76). On the other hand, in a case in whichthe position of the tip has been changed from the position of the tip inthe photoacoustic image of the previous frame in S82 (S82, YES), theprocess of detecting the length direction of the puncture needle 15 inS84 and the process of setting the position and steering direction ofthe ROI in S74 are performed and then color Doppler measurement isperformed (S76).

Then, in S78, the process in S80 to S84 and S74 to S76 is repeatedlyperformed until the user inputs a command to end the detection of theangle of the puncture needle 15. In a case in which the angle detectionend command is input in S78, the process ends.

In the second embodiment, the position of the ROI is controlled suchthat the tip of the puncture needle 15 is located in the ROI. However,the invention is not limited thereto. The position of the ROI may becontrolled such that the tip of the puncture needle 15 is located at aposition that is separated outward from the edge of the ROI by apredetermined distance.

In the above-described embodiments, the puncture needle 15 is used as anembodiment of the insert. However, the invention is not limited thereto.The insert may be a radio-frequency ablation needle including anelectrode that is used for radio-frequency ablation, a catheter that isinserted into a blood vessel, or a guide wire for a catheter that isinserted into a blood vessel. Alternatively, the insert may be anoptical fiber for laser treatment.

The insert according to the invention is not limited to a needle, suchas an injection needle, and may be a biopsy needle used for biopsy. Thatis, the needle may be a biopsy needle that is inserted into aninspection target of the living body and extracts the tissues of abiopsy site of the inspection target. In this case, photoacoustic wavesmay be generated from an extraction portion (intake port) for suckingand extracting the tissues of the biopsy site. In addition, the needlemay be used as a guiding needle that is used for insertion into a deeppart, such as a part under the skin or an organ inside the abdomen.

In the above-described embodiments, a photoacoustic image is generatedon the basis of the photoacoustic waves generated from the photoacousticwave generation portion 15 c. However, in the invention, imaging is notnecessarily performed and the photoacoustic image may be generated indevices other than the photoacoustic measurement device.

The invention has been described above on the basis of the preferredembodiments. However, the insert and the photoacoustic measurementdevice according to the invention are not limited only to theabove-described embodiments. Various modifications and changes of theconfigurations according to the above-described embodiments are alsoincluded in the scope of the invention.

What is claimed is:
 1. A photoacoustic measurement device comprising: aninsert comprising a tip portion configured to be inserted into a subjectand which includes a light guide member that guides light to the tipportion and a photoacoustic wave generation portion that absorbs thelight guided by the light guide member and generates photoacousticwaves; an ultrasound probe that detects the photoacoustic wavesgenerated from the photoacoustic wave generation portion and detectsreflected acoustic waves reflected by transmission of acoustic waves tothe subject; and a processor configured to: generate a color Dopplersignal based on the reflected acoustic waves from a region of interestas a color Doppler measurement target which has been detected by theultrasound probe; generate a reflected acoustic image based on thereflected acoustic waves detected by the ultrasound probe; detect alength direction of the insert based on the reflected acoustic image;control a steering direction of the region of interest based on thelength direction of the insert such that an angle θ formed between astraight line which extends in the length direction of the insert and astraight line which extends in the steering direction of the region ofinterest satisfies 0°≤θ<90°, wherein the processor is further configuredto store a plurality of steering angle candidates of the region ofinterest in advance, select a steering angle at which the angle θsatisfies 0°≤θ<90° and the steering direction of the region of interestis closest to the length direction of the insert from the plurality ofsteering angle candidates, and set the steering direction of the regionof interest to a direction indicated by the selected steering angle. 2.The photoacoustic measurement device according to claim 1, wherein theprocessor is further configured to set the steering direction of theregion of interest, following a change in an insertion direction of theinsert, in a state in which a magnitude of the angle θ is maintained. 3.The photoacoustic measurement device according to claim 1, wherein theprocessor is further configured to set the angle θ to 0°.
 4. Thephotoacoustic measurement device according to claim 1, wherein theprocessor is further configured to: generate a photoacoustic image basedon the photoacoustic waves detected by the ultrasound probe; detect aposition of a tip of the insert based on the photoacoustic image, andcontrol a position of the region of interest such that the tip of theinsert is included in the region of interest.
 5. The photoacousticmeasurement device according to claim 4, wherein the processor isfurther configured to set the position of the region of interest suchthat a center position of the region of interest is matched with the tipof the insert.
 6. The photoacoustic measurement device according toclaim 4, wherein the processor is further configured to set the positionof the region of interest, following movement of the position of the tipof the insert, in a state in which a relative positional relationshipbetween the position of the tip of the insert and the region of interestis maintained.
 7. The photoacoustic measurement device according toclaim 1, wherein the processor is further configured to detect thelength direction of the insert at each interval of two or more frames ofthe reflected acoustic images.
 8. The photoacoustic measurement deviceaccording to claim 7, wherein the processor is further configured toacquire an amount of change in an angle of the length direction of theinsert, and in a case in which the amount of change is equal to or lessthan a predetermined threshold value, increase the frame interval atwhich the length direction of the insert is detected.
 9. Thephotoacoustic measurement device according to claim 1, wherein theprocessor is further configured to: generate a photoacoustic image basedon the photoacoustic waves detected by the ultrasound probe; and detecta position of a tip of the insert based on the photoacoustic image,wherein, in a case in which the position of the tip of the insertdetected is the same as a position of the tip of the insert in thephotoacoustic image of a previous frame, the detection of the lengthdirection of the insert based on the reflected acoustic image and thecontrol of the steering direction of the region of interest based on thelength direction of the insert are not performed.
 10. The photoacousticmeasurement device according to claim 1, wherein the insert is a needleconfigured to be inserted into the subject.